This relates generally to imaging systems and, more particularly, to imaging systems with back side illuminated pixels.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imager sensors (sometimes referred to as imagers) may be formed from a two-dimensional array of image sensing pixels. Each pixel includes a photosensitive layer that receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format.
Pixels may be front-side illuminated or back-side illuminated. In back-side illuminated pixels, processing circuitry may be formed underneath the photosensitive layer so that processing circuitry does not prevent incident light from reaching the photosensitive layer. However, certain back-side illuminated pixels may have a low conversion gain, which may be defined as the change in voltage for each unit of charge accumulated by a photodiode. Pixels with low conversion gain may have excess pixel readout noise and poor pixel performance.
It would therefore be desirable to be able to provide improved back-side illuminated pixels for image sensors.